The present invention relates to a method of finishing a concave spherical pivoting bearing surface on a roller segment having an external rolling surface, the roller segment being intended in particular to form part of a motor vehicle transmission joint.
The present invention also relates to a device for effecting machining of this kind.
The invention relates in particular, but not limitatively, to roller segments intended to form part of a transmission joint comprising three spherical trunnions forming a tripod at the end of one of two shafts connected together by the joint. Depending on the direction of the movement to be transmitted, each spherical trunnion bears, through a roller segment, against one or another of two respective longitudinal rolling tracks provided inside a bowl fixed to the other of the two shafts connected together by the joint. Six roller segments are thus interposed, each between one of the rolling tracks and the respective trunnion. Each roller segment has a concave spherical bearing surface pivoting on the spherical trunnion, and an external toric rolling surface which is able to roll on the rolling track and to be inclined laterally relative to the rolling, which has a concave cylindrical profile. These sliding homokinetic joints possess the properties of comfort and compactness required for equipping modern motor vehicles. They are described in French Patent Application No. 86 17 044 of the 5th December 1986.
The remarkable performance of these joints is to a a large extent due to the hydrodynamic lubrication of the spherical articulation between the spherical trunnion and the concave spherical bearing surface of the segment. This hydrodynamic lubrication practically cancels out the resultant slide drag, while accepting high pressures for the load transfer. The constitution of the extremely thin film of lubricant--taking into account the low speeds of sliding--entails perfect complementarity of the surfaces.
Methods are known for the machining of concave spherical pivoting bearing surfaces which enable only an approximate complementarity to be achieved. These methods therefore entail additional stages of grinding in of the two surfaces, one against the other, by a method used in the production of optical lenses. The need for such grinding in is incompatible with the imperatives of cost, price and production rate of the motor vehicle industry.
The aim of the present invention is, therefore, to provide an industrial means of producing segments having a concave spherical bearing surface with a precision permitting perfect complementarity with the spherical trunnions of the tripod which are intended to cooperate with these segments, and therefore allowing hydrodynamic lubrication by a micrometric lubricant film in the homokinetic joint, without requiring grinding in.